In an image forming device, the following processes are performed: (1) an electrostatic latent image is formed on a surface of a photoreceptor drum, which is uniformly charged by a charge roller, through exposing the surface by an exposure head; (2) the electrostatic latent image is developed by a thin layer of toner that is formed on a developing roller, so that a toner image is formed on the photoreceptor drum; and then (3) the toner image is transferred and is fused on a sheet of paper. For example, in an image forming unit that uses a single-component contact development system, toner is supplied from a toner cartridge. The toner is charged by frictional charge generated between a supply roller and a developing roller and between a regulation blade and the developing roller. Then, a thin toner layer is formed on the developing roller by the regulation blade.
The developing roller is configured to contact the photoreceptor drum, and charged toner is transferred on the electrostatic latent image so that the toner image is formed by charged toner and is created by an electric field formed on the surfaces of the developing roller and the photoreceptor drum. For example, in a direct transferring system in which the toner image on the photoreceptor is directly transferred to a sheet that is carried by a transferring belt, the toner image that is moved in a transferring area by the rotation of the photoreceptor drum is transferred to a sheet by electric field.
In the image forming device discussed above, when the toner image is transferred on the sheet from the photoreceptor drum by impressing a certain amount of charge to the toner, the following problems may occur. If the toner image is insufficiently charged, the toner image might not be transferred on the sheet but may remain on the photoreceptor drum. Toner that is damaged through repeated friction and an externally added agent, which is separated from toner, may be clumped together (agglomerated) and may adhere to the photoreceptor drum. Foreign particles and so on that are adhered to the transferring belt and the sheet may adhere to the photoreceptor drum.
Residual materials on the photoreceptor drum, such as residual toner or foreign particles, are collected by a cleaning device that is located at the downstream end of the transferring area in the photoreceptor drum. However, when the residual materials are heavily adhered to the photoreceptor drum, the residual materials cannot be completely removed from the photoreceptor drum with the cleaning device. As a result, the residual materials remain on the drum and create a film. The materials cause an image defect (or deteriorate the quality of the print image). In a conventional image forming device, a cleaning member is attached to a drum shutter that functions to protect the surface of the photoreceptor drum when an image forming unit is detached from the image forming device with a purpose of removing the residual toner and preventing the residual toner on the photoreceptor drum from creating a film. The residual toner and so on are removed by sliding the cleaning member on the surface of the photoreceptor drum when the drum shutter opens and closes at the time of detaching and attaching the image forming unit. See Japanese laid-open patent application publication number 2001-324910, especially, paragraphs 0025-0027 and FIGS. 3 and 4.
In the conventional technology discussed above, because the cleaning member is attached to the drum shutter and because the residual toner and so on are removed by the cleaning member sliding on the surface of the photoreceptor drum when the drum shutter opens and closes at the time of detaching and attaching the image forming unit, the areas that can be cleaned are restricted to the areas that the cleaning member, which is attached to the drum shutter, can contact. When the foreign particles and so on are adhered to the entire surface of the photoreceptor drum, the residual materials on the photoreceptor drum cannot be completely removed. Therefore, there is a problem that image defects may occur.
An object of the present invention is to provide an image forming device that can completely remove the residual materials even though the residual materials are adhered to the entire (circumferential) surface of an image carrier, such as the photoreceptor drum.